Lyle Denniston at Scotusblog.com has a rundown of the cases, which stemmed from the arrest of a suspected gang member in California and a suspected drug dealer in Massachusetts.

Police have long been able to search a suspect and their immediate surroundings under the notion of "incident to arrest," aimed at securing any weapons and preventing destruction of possible evidence.

The same incident to arrest claim has been expanded to include searches of cell phones and other digital devices, the Electronic Frontier Foundation argues. The San Francisco-based electronic privacy group argues police should obtain a search warrant, showing probable cause, if they want access to cell phone content.

Given how much information, much of it personal, can be contained on modern smart phones, the court is being asked to spell out limits to the searches.

The New York Times also writes about the issue today and provides this framing:

"The justices will have to decide how to apply an 18th-century phrase -- the Fourth Amendment's prohibition of "unreasonable searches and seizures" -- to devices that can contain 100 times more information than is in the Library of Congress's 72,000-page collection of James Madison's papers," the Times' Adam Liptak writes.